Filter United VIVA21 6-Stage Complete Replacement Filter Set (V21RF6S12PH)
The full six-cartridge rebuild for the VIVA21 at $99.99, including the alkaline remineralization stage that costs $49.99 on its own.
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QUICK VERDICT
One $99.99 box rebuilds the entire VIVA21 filter train, including the alkaline remineralization cartridge that is $49.99 bought alone.
Price: $99.99 · Verified: 2026-08-14
One $99.99 box rebuilds the entire VIVA21 filter train, including the alkaline remineralization cartridge that is $49.99 bought alone.
This is the full cartridge set for the VIVA21 6-stage system: the 5-micron sediment filter, both 5-micron extruded carbon blocks, the 50 GPD TFC reverse osmosis membrane, the coconut shell post-carbon filter, and the alkaline remineralization cartridge, at $99.99 against a $139.99 compare-at. The 5-stage equivalent is $79.99. Bought piecemeal, the alkaline cartridge alone is $49.99 and Filter United rates it for 18 months of normal household use. The brand's own change schedule is sediment and carbon about every 12 months and the membrane and inline carbon every 2 to 3 years, which is why it also quotes roughly $40 to $80 a year in consumables rather than the full set price annually.
The cross-compatibility claim is the part to read carefully. Filter United states these cartridges fit all standard under-sink reverse osmosis systems and names APEC, Express Water, and iSpring by name on its own pages. That is a self-declared fit claim, not a certified compatibility list, and there is no published cross-reference chart, so if you are buying these for a system that is not a VIVA21, measure your housings and confirm with Filter United before ordering. The same certification caveat applies here as on the system: the WQA Gold Seal and NSF 58 and 372 language is the brand's claim, published without a certificate number, and we could not verify it independently.
The clean fit is a VIVA21 owner doing an annual or biennial rebuild, where one $99.99 box replaces the whole train and there is no fit question at all. The second fit is a cross-shopper with another under-sink RO system who is willing to check housing sizes themselves before ordering.
VIVA21 owners rebuilding the full filter train in one purchase, and cross-shoppers with another under-sink reverse osmosis system who will verify housing fit themselves before ordering.
You want a certified compatibility list for a non-VIVA21 system, or you only need the one cartridge that is actually due, since the sediment and carbon stages and the membrane run on different schedules.
Specifications
Where this fits
Filter United VIVA21 6-Stage Complete Replacement Filter Set (V21RF6S12PH) cross-shops across several editorial surfaces on this site: the full brand catalog and the in-depth guides for its category.
Filter United VIVA21 6-Stage Complete Replacement Filter Set (V21RF6S12PH) - buyer FAQ
what filters come in the viva21 6 stage replacement set
The V21RF6S12PH set contains six cartridges: one 5 micron sediment filter, two 5 micron extruded carbon block filters, a 50 GPD high-rejection TFC reverse osmosis membrane, a coconut shell post-carbon polishing filter, and an alkaline mineral restoration cartridge. It is the full stack, so you are not buying the membrane separately. The set ships at a listed 6.0 lb.
how often should i replace the viva21 filter set
Filter United lists 6 to 12 months for the first three stages, 12 months for the coconut shell post-carbon filter, and 24 to 36 months for the RO membrane. That means the membrane in this set outlasts one to two rounds of pre-filters, so buying the complete 6 filter set every year replaces a membrane that may still have life in it.
does the viva21 filter set fit apec ispring or express water systems
The set is described as compatible with all standard under-sink reverse osmosis systems and traditional RO units using 10 inch housings. Filter United's FAQ page separately says it offers customized compatible filters for APEC, Express Water and iSpring systems, which suggests those may need a different part rather than this exact 6 filter set. Confirm your housing length first.
do i need a subscription to buy replacement filters
No. The set is sold outright as a one-time purchase. Filter United runs an optional auto-ship program that its site advertises at 15% off filters, and its FAQ page also mentions an optional smart TDS monitor that signals when a change is due. Nothing about the hardware locks out of a plain one-off order.
is the alkaline stage in this set the same as the standalone v21rfph filter
The set page only says stage 6 is a mineral restoration cartridge that raises pH, with a 12 month interval implied by the post-filter schedule. The separately sold V21RFPH alkaline cartridge is described as a 10 inch, 1/4 inch quick-connect unit adding calcium carbonate with 18 months of capacity. Filter United does not state on either page that the two are identical.
Filter United VIVA21 6-Stage Complete Replacement Filter Set
$99.99 · Verified 2026-08-14
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